As a process for producing a color filter, a dyeing method, a pigment dispersion method, a printing method, an ink jet method and an electrodeposition method are known at present.
In the dyeing method, a water soluble polymer film is formed on a glass substrate, and the water soluble polymer film is patterned into a desired shape through a photolithography process. The substrate is then immersed in a dyeing solution to obtain a pattern of the dyed water soluble polymer. These steps are repeated for each colors, red (R), green (G) and blue (B), to obtain a color filter layer. The filter thus obtained has a high transmissibility and large variety of colors. Since the dyeing method is highly sophisticated, this method is often used in a color solid state imaging device (CCD). However, this method is inferior in light resistance because a dye is used, and the numbers of steps in the production process are large. Therefore, in recent years, a pigment dispersion method is employed for the production method of a liquid crystal display device (LCD) instead of the dyeing method.
The pigment dispersion method is the recent main stream of the production method of a color filter. In this method, a resin layer having a pigment dispersed therein is formed on a glass substrate, and the resin layer is patterned through a photolithography process. This is repeated for each colors, R, G and B, to obtain a color filter layer. While the pigment dispersion method is sophisticated, it is disadvantageous in that the numbers of steps in the process are large, and the production cost is high.
In the printing method, a step of printing an image on a substrate by using a thermosetting resin having a pigment dispersed therein is repeated for each colors, R, G and B, and the resin on the substrate is hardened by heating, to obtain a color filter layer. In this method, a photolithography process is not necessary in the formation of the R, GandB layers, but the resolution and the uniformity in film thickness are inferior.
In the ink jet method, after an ink receiving layer has been formed on a substrate with a water soluble polymer, a part of the ink receiving layer is treated to be hydrophilic, and the other part is treated to be hydrophobic, followed by spraying an ink to the hydrophilic part, to obtain a color filter layer. In this method, a photolithography process is not necessary in the formation of the R, G and B layers, but the resolution is low because the minimum pixel size is determined by the size of a droplet of the ink. Furthermore, there is a high possibility in this method that droplets of the ink is scattered to produce mixed colors between the filter layers adjacent to each other, and the yield is low.
In the electrodeposition method, a high voltage of about 70 V is applied to a transparent electrode, which has been patterned, in a electrolytic solution having a water soluble polymer and a pigment dispersed therein, to form an electrodeposition film on the electrode. These steps are repeated for each colors, R, G and B, to obtain a color filter layer. In this method, it is necessary to previously pattern the transparent electrode used as an electrode for electrodeposition by photolithography, and it cannot be used for producing a color filter of a TFT liquid crystal display because the shape of the pattern is restricted.
In a color filter of a liquid crystal display, each pixel as a micro-cell generally should be covered with a black matrix, and photolithography is generally employed for producing the black matrix. However, although fine production precision can be obtained by this method, it requires a large number of steps and a large equipment cost, which result in increase in cost. Therefore, a simple process for producing a color filter without using photolithography is demanded.
On the other hand, documents containing color images widely spread throughout society, and a demand for high resolution, is being increased along with the development of a CPU. In order to satisfy the demand, a printing method using light is proposed, and a simple technique is also demanded in production of a color filter.
Various proposals have been made for a method for forming an image by utilizing light. For example, a method for recording an image is reported in H. Yoneyama, et al., J. Electrochem. Soc., p. 2414 (1985), in which pyrrole is electrolytically polymerized by irradiating with light on a Si substrate, and an image is formed by doping and dedoping of the resulting polypyrrole. This method for recording an image using polypyrrole has an advantage in that it can be conducted with a low voltage of 1.0 V or less. However, this method utilizes the color owned by polypyrrole itself and is not suitable for producing a color filter. Furthermore, a thin film cannot be produced by this method. As a method of utilizing light in the production of a color filter, JP-A-5-119209 and JP-A-5-157905 disclose a method, in which a semiconductor maintaining an exposure effect for a certain period (i.e., a semiconductor having a photo-memory property) is irradiated with light, and the semiconductor is immersed in an aqueous electrodeposition solution with applying a voltage of from 20 to 80 V, to obtain a filter layer. This method utilizes an outer photoelectric effect, in which a semiconductor is irradiated with light to increase an electric current that appears on application of a high bias voltage to the semiconductor, so as to increase the conductivity of the semiconductor. However, unevenness in electric current density is liable to be formed, and it is difficult to form a uniform film with good quality.